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The Coriolis effect: The Spinnining.

Hey there folks - long time no see. Howdy Murray! I recently had an experience with aquaculture that I wrote about, so I thought I would compile it and paste it here. For me, it was illuminating.

"About ten years ago I started using large HDPE rain water tanks available in Australia for large scale aquaculture. They are almost perfectly cylindrical ('roto-moulding') and range in size from 3,000 to 50,000 liters. It appears that they rotate water in a clockwise direction, and I cannot understand why. I must admit to being mildly embarrassed and more than a little frustrated. I have always secretly prided myself on my basic understanding of physical forces, but for me the mystery persists and I can barely tolerate this. I have my suspicions, but I have been around aquaculture and bodies of water too long not to properly understand this.

So here is my problem. After the sun comes up I have to go and physically trip a switch to enable power to the aquaculture tanks on a renewable energy system with a flaw that I am too lazy to repair. Every day, I momentarily get to view the aquaculture tank in its serene tranquility. Perfectly clear, highly oxygenated, cold water with zero mechanical input - slowly rotating in a clockwise direction at roughly 1 meter-per-minute at the extremity. The rotation is slow enough that you will not notice it without examination.

It is not due to the mechanical agitation of the fish. The density is far too low for that, and the species involved do not 'school' or point in a specific direction. Their behavior is very random, scattered amongst various submerged 'habitats'. The pumps turn off before dusk and there are no leaks. It is a 'closed' recirculating system.

I considered that thermal distribution caused by the moving sun could effect circulation, but I could not comprehend why this should be such that the entire body of water always rotates in a clockwise direction.

Whichever way - it is a pleasant surprise from an applied science perspective. My instant and first realisation as an aquacultural engineer was that I was receiving free water circulation. Any movement of water (can*) dissipates thermal layers developing in bodies of water, assisting in avoiding anoxic zones. I long ago noticed that oxygen levels were maintained at a healthy level throughout the night - even at the bottom, even without circulation. But I had no good mechanism to explain this - other than low water temperatures.

So what is going on here? The Coriolis effect? Can a still/standing body of water begin rotating in a large cylinder? In the southern hemisphere, the Coriolis effect does work in a clockwise direction. If so, how could it be that aquaculture literature has not addressed this? Too much cheap energy for too long? My imagination gone wild? Is this free circulation?

Notes:

Clearly if this is a real observed phenomenon, then the same forces are likely in a similarly shaped glass containing 350mls of water. Yet no rotation is observed. I can invoke various reasons to explain this, such as the idea that surface tension and friction can overcome rotational forces in low-radius cylinders. But does a large radius, multi-tonne, disk-shaped cylinder of water have the mass to achieve rotation inside a smooth vessel? The bodies of water are all within 0.9-1.5m deep and have a radius of 1.3-2.8m, weighing from 1.5 to 25 tonne. Is it momentum from the pumps? It does not compute to me that the water could rotate from its own inertial forces for that amount of time. There are many submerged obstacles to dissipate the energy and the rotation observed from the pumps clearly dissipates in minutes once the power is removed. The idea that this momentum could persist for 13hrs strains credulity?

If this is the Coriolis effect - which is my current leading suspicion - then it is remarkable that the advantages are not often discussed and leveraged in sustainable recirculating aquaculture. While I know of the effect, the idea that this is a usable source of energy - a significant one in aquaculture - completely astonishes me. None of my peers or contemporaries have ever spoken of it to me personally. Yet anyone using cylindrical tanks is subject to its effects.

For example, this means all recirculating aquacultural tanks in the southern hemisphere should be configured to rotate in a clockwise fashion. That seems kind of important. But with all my experience and knowledge, I have had to work it out myself. That makes very little sense to me. Why is this something I just realised?

A cylindrical body of water of a sufficient size can start to spontaneously rotate in a vortex and nobody told me? In aquaculture?

I am having serious problems working out if this is true or not!

UPDATE: I am now basically convinced that this is the Coriolos effect rotating the water, although I lack the resources to run a controlled experiment to prove it. Standing bodies of water of the right shape and size will spontaneously begin a slow vortex - clockwise in the southern hemisphere, anti-clockwise in the northern hemisphere. This is an important realisation for any aquacultural engineer and I am amused if not somewhat concerned as to have never come across this discussed by anyone before in my extensive history of aquacultural experience.

Low-energy, sustainable aquaculture is one of the main goals for the future of mankind. The Coriolis effect will be an important contribution."

TL;DR: If you build a cylindrical body of water of sufficient size and shape, it will spontaneously begin to rotate inside a fixed vessel. If you build an aerofoil along the bottom of the cylinder, it will create both lift and circulate the water layers.

The direction and strength of the rotation is dependent on your location on the surface of the planet. It is 'free' energy, however you will slightly slow down the rotation of the planet - so just don't all do it at once.

Oh also Murray - I finished my diploma! Agriculture and Technology - Aquaculture. One more year to go (degree). Then another (honours). Then maybe 2 more (PhD scholarship?). Or until I get a good job in the industry. Whatever

The direction and strength of the rotation is dependent on your location on the surface of the planet. It is 'free' energy, however you will slightly slow down the rotation of the planet - so just don't all do it at once.

Click to expand...

I guess I'm fighting the laws of nature in my fingerling tank when I set the flow in water to spin the water anti clockwise. Its only 750l circular so I don't think I'll flip the earth's axis or anything.

Oh also Murray - I finished my diploma! Agriculture and Technology - Aquaculture. One more year to go (degree). Then another (honours). Then maybe 2 more (PhD scholarship?). Or until I get a good job in the industry. Whatever